Facebook: Five things to avoid

Joanne Fraill, the juror who contacted a defendant on Facebook, is facing a spell in jail for contempt of court when she is sentenced later on Thursday.

She has learned the hard way, but for the rest of us there are some essential "don'ts" if you want to stay out of trouble on Facebook. Don't...

...make friends with people you shouldn't

Men attracted to amputees befriended Charlotte Fielder

Add as a friend? Think before clicking "confirm". Ms Fraill didn't. The juror said it was empathy that led her to track down Jamie Sewart - a defendant in a drugs trial - on Facebook and later become "friends" with her. The contact was disclosed to the judge and in less than a year Ms Fraill was back in court, this time in the dock.

While this case is a first in the UK to involve the internet, it is not the first time Facebook users have picked the wrong friends - and certainly won't be the last. Nathan Singh, a prison officer at HMP Leicester, was shown the door after serving inmates were found to be among his Facebook friends.

But bad choices are not always obvious. Charlotte Fielder, who was born missing a hand, unwittingly befriended men on Facebook who pretended to have lost a limb themselves, but were, in fact, sexually attracted to amputees. Later, she found her profile image had been copied and posted onto a pornographic website, where obscene comments were made.

...moan about your boss/customers/constituents

Warring parties should keep it political on Facebook, not make it personal

It sounds obvious but is surprisingly common. A woman, known only as Lindsay, declared in a status update, "OMG I hate my job!" before launching into a personal attack on her boss. It was a matter of hours before she was reminded that her boss was among her "friends". He reportedly posted a response telling Lindsay not to bother coming in tomorrow. "I'll pop your P45 in the post. And yes, I'm serious," he wrote.

Virgin was also filling out P45s after airline cabin crew called their passengers "chavs" and said Virgin planes were full of cockroaches and engines were replaced four times a year. Their careers took a swift nosedive when 13 of them got the sack.

Politicians, in particular, seem prone to this pitfall. However impassioned your beliefs, it's ill-advised to make politics personal as Welsh assembly candidate Joe Lock learned. Last year, he placed a link to a Facebook group called Is Margaret Thatcher Dead Yet? with the comment, "Can't be long, fingers crossed." The Tories found the remarks "offensive" and "unacceptable for anyone seeking public office", and Mr Lock humbly apologised.

A Blackpool Labour councillor was also forced to eat his words after calling his own constituents "donkey-botherers" in a football jibe on Facebook that could be viewed by everyone. The Tories wrongly predicted "political suicide" - Simon Blackburn is now leader of the council.

A Kent Conservative election candidate prospered less well after he called local women "sluts". In a Facebook discussion, Payam Tamiz wrote that he wanted to settle down with "someone decent" but it was "impossible to find someone with morals and a bit of self-respect". After an unreserved apology, he resigned.

...upload dodgy photos

Sean Aspey's birthday celebrations turned sour over his costume choice

Unless you look after your privacy settings, embarrassment and shame are almost inevitable on Facebook - from the mildly upsetting double-chin shot to one of glazed-over eyes and hand clamped to a wine bottle in some dark den.

If Sir John Sawers, whose position as head of MI6 would suggest someone adept at keeping things out of the public eye, can fall foul, then aren't we all in danger? His wife posted holiday snaps, including Sir John in Speedo trunks, alongside details about their children and the location of their flat. The details and photos were swiftly removed from the site - but it takes longer for images to fade from the collective memory.

A Lib Dem councillor in Wales had little to laugh about after his 'Allo 'Allo-themed birthday party. Sean Aspey posted on Facebook photos of himself, dressed as a Nazi officer from the TV comedy set in Nazi-occupied France. He was suspended from Porthcawl town council - not the best end to anyone's 40th birthday celebrations.

...enjoy your sick leave too much

If you've pulled a sickie or are genuinely ill, it's probably best to stay off Facebook. A Canadian woman on long-term sick leave for depression says she lost her benefits when her insurance agent found photos of her enjoying herself on Facebook, seemingly having fun in the sun and late nights out with friends. Nathalie Blanchard had been on leave from her job at IBM in Quebec for a year and maintains her activities were on doctors' orders as a way to beat depression.

Another woman lost her job when bosses spotted she was using Facebook, having earlier told them she was too ill to use a computer. The unnamed Swiss worker told her employer, Nationale Suisse, she had a migraine and needed to lie in a darkened room. She claimed she had been accessing the internet on her iPhone while in bed.

...spill secrets

Mum's the word: The MoD wants service families to watch what they say on Facebook

You can't exactly whisper on Facebook, so secrets are best confined to corridors and corners.

Israel was among the first to get nervy about sensitive information appearing on the internet after a review of its troops' Facebook pages revealed detailed pictures of air bases, operations rooms and submarines. A new set of rules - which was not made public - included a ban on images of pilots and special unit members, and anything showing specific military manoeuvres.

The UK's Ministry of Defence is similarly concerned and has launched a campaign to encourage its personnel, and their friends and family, not to share sensitive information. In a video for the campaign, a mother is seen posting information about her son's forward operating base on Facebook - and is then seen having tea with an armed man in a balaclava.